http://blogs.zdnet.com/microsoft/?p=3053

Sharepoint 2007 has some good premises for SaaS like software deployment.

One of these would be the permissions the user has to only view/edit and delete the own items in a list. Imagine a HelpDesk or a CRM where a Company only "sees" it's own stuff, and within the company each user his/her own.

How could it be even better?

If it was easier to set item level permissions to isolate and restrict different Sharepoint groups to be able to see only their "items" in a list and each user in the group only his/her own, bar the groups admin seing all of the groups items.

That would make Sharepoint Saas by default.